The invention relates to an operating device for operating at least one electric lamp and to an operating method for at least one electric lamp.
There are commercially available operating devices, termed dimmable electronic ballasts (EVGs) for operating electric lamps which permit a dimmed operation, that is to say brightness control of the lamps connected thereto, in particular fluorescent lamps or halogen incandescent lamps. These dimmable operating devices have a control input to which a voltage serving as setpoint for brightness control can be applied. The control input is usually constructed as a 1-10 V interface. In the simplest case, a dimming potentiometer is connected to this control input in order to set the brightness of the lamp, operated using the operating device, to the setpoint. With the aid of the dimming potentiometer and with the aid of a transformer excited by a voltage varying periodically with time, a voltage with a value of between 1 V and 10 V which represents the setpoint for the desired brightness setting is generated at the control input. This voltage is transmitted to an evaluation device in the operating device by means of the transformer. Moreover, the transformer also effects electrical isolation between the control input and the evaluation device in the operating device. With the aid of a peak value rectifier, the evaluation device generates a signal, corresponding to the setting at the dimming potentiometer, for controlling the lamp current or the power consumption of the lamp, or for controlling the output power of the operating device. The properties of the transformer, in particular its leakage inductance, exert a large influence on the voltage transmitted to the evaluation device. A high leakage inductance of the transformer causes disturbing voltage pulses on the transmitted voltage which are interpreted by the evaluation device as controlled variables. Use has therefore been made so far of specifically constructed toroidal core transformers which have a low leakage inductance, and moreover a lowpass filter has been connected upstream of the evaluation device in the operating device in order to reduce voltage peaks.
It is the object of the invention to provide an operating device for operating at least one electric lamp, which has an improved evaluation device for evaluating the voltage present at the control input and transmitted by the transformer. It is also the object of the invention to provide an improved method for operating at least one electric lamp connected to an operating device for electric lamps which has a control input for prescribing an electric voltage serving as setpoint for controlling an operating parameter of the at least one electric lamp.
These objects are achieved according to the invention by means of the features of the independent patent claim 1 and the independent patent claim 7. Particularly advantageous designs of the invention are described in the dependent claims.
The operating device according to the invention for operating at least one electric lamp has a control input to which an electric voltage can be applied which serves as setpoint for controlling an operating parameter of the at least one electric lamp, and has a transformer which is provided for transmitting to an evaluation device the electric voltage which is impressed on the control input and serves as setpoint for controlling an operating parameter of the at least one electric lamp and having an oscillator for exciting the transformer with an electric voltage changing periodically with time. According to the invention, the evaluation device has a sample-and-hold element. Moreover, means are provided for matching the frequencies of the sequence signal of the sample-and-hold element and the electric voltage changing periodically with time, and for producing a temporary constant phase shift between the sequence signal of the sample-and-hold element and the electric voltage changing periodically with time, in order to remove peaks in the voltage transmitted by the transformer. Owing to these measures, it is possible to use cost effective transformers with a comparatively high leakage inductance as transformers in the operating device. Moreover, it is possible to dispense with a lowpass and a peak value rectifier for evaluating the voltage transmitted by the transformer.
The sample-and-hold element is advantageously constructed as a constituent of an analog to digital converter in order to generate a digital control signal for a microcontroller or an integrated circuit which serves to control the operating device. The transformer serving as transformer advantageously has a first winding which is connected to the control input, and has at least one second winding which is connected to the evaluation device and coupled magnetically to at least one first winding. Electrical isolation is thereby ensured between the control input and the evaluation device.
The means for matching the frequencies of the sequence signals of the sample-and-hold element and the electric voltage changing periodically with time, and for producing a constant time shift between the sequence signal of the sample-and-hold element and the electric voltage changing periodically with time advantageously comprised
an oscillator for generating the sequence signal,
a frequency divider for halving the frequency of the electric voltage changing periodically with time, and
a device for matching the frequency of the sequence signal to the electric voltage changing periodically with time, and for producing the constant time shift.
An AND gate is advantageously used as device for the frequency matching of the sequence signal to the electric voltage changing periodically with time, and for producing the constant time shift. Any peaks on the voltage transmitted by the transformer can be removed in this way cost-effectively and with simple means.
The operating method according to the invention is distinguished according to the invention in that the voltage at the transformer is fed to a sample-and-hold element for the purpose of evaluation, in order to remove peaks in the voltage of the transformer with the aid of the sample-and-hold element. Advantageously, in order to evaluate the voltage at the transformer the frequencies of the electric voltage varying periodically with time and of the sequence signal of the sample-and-hold element are matched, and the sequence signal of the sample-and-hold element is delayed by a constant time interval by comparison with the electric voltage varying periodically with time. The sequence signal of the sample-and-hold element is synchronized by this measure with the part of the voltage present at the transformer which has been transmitted without disturbance. A particularly simple and cost effective operating method is disclosed in claim 7. In accordance therewith, the following method steps are carried out in order to evaluate the voltage at the transformer:
using an oscillator to generate the sequence signal and the electric voltage varying periodically with time,
using a frequency divider to halve the frequency of the electric voltage varying periodically with time,
matching the frequency of the sequence signal to the frequency of the electric voltage varying periodically with time, and generating a constant time shift between the sequence signal and the electric voltage varying periodically with time,
applying the electric voltage varying periodically with time to the transformer, and
transmitting the voltage at the transformer to the sample-and-hold element as input voltage.
The output voltage of the sample-and-hold element is advantageously used to control the operating parameter of the at least one electric lamp, or converted in advance into a digital signal by means of an analog-to-digital converter.